table(mapped$col2) ------------------------------------------------------------------- Jacques VESLOT
CNRS UMR 8090 I.B.L (2ème étage) 1 rue du Professeur Calmette B.P. 245 59019 Lille Cedex Tel : 33 (0)3.20.87.10.44 Fax : 33 (0)3.20.87.10.31 http://www-good.ibl.fr ------------------------------------------------------------------- michael watson (IAH-C) a écrit : > Hi > > I have a data.frame, two columns, 12304 rows. Both columns are factors. > I want to do an equivalent of an SQL "group by" statement, and count the > number of rows in the data frame for each unique value of the second > column. > > I have: > > countl <- by(mapped, mapped$col2, nrow) > > Now, mapped$col2 has 10588 levels, so this statement takes a really long > time to run. Is there a more efficient way of doing this in R? > > Thanks > > Mick > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.